All the auxiliary verbs except "be, do and have" are called modal verbs. Unlike other auxiliary verbs, modals only exist in their helping form; they cannot act alone as the main verb in a sentence.
Be, do, and have also differ from the other auxiliaries in that they can also serve as ordinary verbs in a given sentence.
The modal verbs are: can, could, may, might, must, shall, should, ought to, will and would.